Project overview
Creeping perennial weed species, including Canada thistle and field bindweed, are among the most difficult weeds to manage in organic agricultural systems due to their persistence, proliferation, and detrimental impacts to crop yields. Frequent tillage is a common strategy deployed by organic farmers to manage creeping perennial weeds, but this practice can also pose several environmental challenges (i.e., soil aggregate degradation, depletion of critical soil water reserves, and increased erosion). Cover cropping with alfalfa is another common strategy, as alfalfa stands are highly competitive and can provide both weed suppression and revenue as a forage crop. However, alfalfa is a highly water-intensive crop and can deplete critical soil water reserves, thereby reducing subsequent crop yields. As such, there is a need to identify alternative methods of controlling/managing creeping perennial weeds in organic production systems.
This study assessed the weed suppressive ability of three highly diverse four-year cropping systems (including a variety of cash crops and cover/forage crops) as potential alternatives to intensive tillage and alfalfa cover cropping.
Farmer takeaways
- Three years of alfalfa consistently outperformed two alternative annual cropping sequences (LENCL and CCPLY) for creeping perennial weed suppression (Canada thistle, sowthistle, and bindweed), demonstrating that – despite its nature as a water-intensive crop – alfalfa remains a good choice for creeping perennial weed management in organic production systems.
- When selecting a cash crop or over crop, farmers should compare the competitiveness of the emerging crop with that of creeping perennial weeds; lentil, for example, proved to be weakly competitive, as were the dominant emergent species (grasses) in the cover crop mixes.
Project objectives and approach
Assess the creeping perennial weed suppressive ability of several diverse, four-year cropping systems and tillage frequencies, as a potential sustainable alternative to intensive tillage and alfalfa cover cropping
- Field studies were conducted at two certified organic sites in North Dakota between 2019 and 2022. Both sites were infested with creeping perennial weeds, but differed regarding species community composition.
- The three four-year cropping systems treatments were: (1) ALF, three years of alfalfa followed by a fourth year of hard red spring wheat (HRSW); (2) LENCL, lentil during the first year, HRSW interseeded with yellow sweet clover the second year, yellow sweetclover green manure the third year, and HRSW the fourth year; and (3) CCPLY, a nine species cool-season cover crop (CC) polyculture the first year, HRSW the second year, a nine-species cool and warm season CC the third year, and HRSW the fourth year.
- The nine species cover crop polycultures included three species each from grass, legume, and brassica functional groups.
- Data was collected on perennial weed, ‘other’ weed, and crop densities at three times each growing season: peak weed emergence, peak weed vegetative growth, and post-harvest.
Key findings
Of the cropping systems assessed, alfalfa provides the greatest creeping perennial weed suppressive properties, with both the lentil and nine-species annual cover crop mix treatments performing variably
- Results from every weed sampling period indicated that the ALF treatment was associated with declines in Canada thistle density and biomass from 2019 to 2021, whereas the LENCL and CCPLY cropping systems generally had consistent Canada thistle infestations.
- The nine species annual cover crop mixes were reasonably competitive against Canada thistle during one of the experimental years (2019), when there was no statistical difference in Canada thistle density between the ALF treatment and the CCPLY treatment.
- Weed suppression associated with annual crops and cover crops (the LENCL and CCPLY treatments) depended primarily on planting timing and the growth habit of the crop, with early plantings resulting in a more successful suppression of Canada thistle. In general, the lentil stands were weakly competitive against weeds.
- ALF was superior to LENCL and CCPLY for managing perennial sowthistle.
- Bindweed density at both peak weed emergence and post-harvest indicated lower field bindweed densities associated with ALF compared to LENCL and CCPLY.
Resources
Gramig, G., Z.A. Pull, and P.M. Carr. 2024. Diversified crop sequencing for suppression of creeping perennial weeds in organic production systems. Farming System 2:100070.
Read MoreLocation
North DakotaCollaborators
Zachary Pull
Patrick Carr
Region
North Central
Topic
Weed Management
Category
Grain and Field Crops, Hay and Pasture
Year Published
2024
